1. Cryptography Chapter 3 Copyright Pearson Prentice Hall 2013

2.  Explain the concept of cryptography.  Describe symmetric key encryption and the importance of key length.  Explain negotiation stage.  Explain initial authentication, including MS-CHAP.  Describe keying, including public key encryption.  Explain how electronic signatures, including digital signatures, digital certificates, and key-hashed message authentication codes (HMACs) work.  Describe public key encryption for authentication.  Describe quantum security.  Explain cryptographic systems including VPNs, SSL, and IPsec. 2 Copyright Pearson Prentice Hall 2013

3. 3

4.  Chapter 1 introduced the threat environment  Chapter 2 introduced the plan-protect- respond cycle and covered the planning phase  Chapters 3 through 9 will cover the protection phase  Chapter 3 introduces cryptography, which is important in itself and which is used in many other protections 4 Copyright Pearson Prentice Hall 2013

5. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 5 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

6.  Cryptography is the use of mathematical operations to protect messages traveling between parties or stored on a computer  Confidentiality means that someone intercepting your communications cannot read them 6 ??? Copyright Pearson Prentice Hall 2013

7. Copyright Pearson Prentice-Hall 2010  Confidentiality is only one cryptographic protection  Authentication means proving one’s identity to another so they can trust you more  Integrity means that the message cannot be changed or, if it is changed, that this change will be detected 7

8.  Plaintext ◦ The message being sent  Encryption ◦ Cryptographic process that changes plaintext into random (seemingly) bits  Ciphertext  Decryption ◦ Cryptographic process that changes ciphertext back into plaintext  Cipher ◦ Mathematical process used to encrypt and decrypt  Key ◦ Use in the cipher ◦ Random string of 40-4,000 bits Copyright Pearson Prentice-Hall 2010 8

9.  Encryption for confidentiality needs a cipher (mathematical method) to encrypt and decrypt ◦ The cipher cannot be kept secret  The two parties using the cipher also need to know a secret key or keys ◦ A key is merely a long stream of bits (1s and 0s) ◦ The key or keys must be kept secret  Cryptanalysts attempt to crack (find) the key 9 Copyright Pearson Prentice Hall 2013

10. 10 Copyright Pearson Prentice Hall 2013

11. Copyright Pearson Prentice-Hall 2010 11 PlaintextKeyCiphertext n4r o8w w15l i16… s23… t16… h3… e9… t12… i20… m6… e25… n o p q r +4 This is a very weak cipher Real ciphers use complex math This is a very weak cipher Real ciphers use complex math Symmetric because both sender and receive must know the key

12.  Substitution Ciphers ◦ Substitute one letter (or bit) for another in each place ◦ The cipher we saw in Figure 3-2 is a substitution cipher  Transposition Ciphers ◦ Transposition ciphers do not change individual letters or bits, but they change their order  Most real ciphers use both substitution and transposition 12 Copyright Pearson Prentice Hall 2013

13. 13 Key (Part 1) Key (Part 2)132 2now 3ist 1het Key = 132 231 Copyright Pearson Prentice Hall 2013

14.  Ciphers can encrypt any message expressed in binary (1s and 0s) ◦ This flexibility and the speed of computing makes this ciphers dominant for encryption today  Codes are more specialized ◦ They substitute one thing for another ◦ Usually a word for another word or a number for a word ◦ Codes are good for humans and may be included in messages sent via encipherment 14 Copyright Pearson Prentice Hall 2013

15. 15 MessageCode From17434 Akagi63717 To83971 Truk11131 STOP34058 ETA53764 6 PM73104 STOP26733 Require29798 B72135 N54678 STOP61552 Transmitted: 174346371783971… Transmitted: 174346371783971… Copyright Pearson Prentice Hall 2013

16. 16 Key Length in Bits Number of Possible Keys 12 24 416 8256 1665,536 401,099,511,627,776 5672,057,594,037,927,900 1125,192,296,858,534,830,000,000,000,000,000,000 1125.1923E+33 1683.74144E+50 2561.15792E+77 5121.3408E+154 Each extra bit doubles the number of keys Each extra bit doubles the number of keys Shaded keys are Strong symmetric keys (>=100 bits) Shaded keys are Strong symmetric keys (>=100 bits) Copyright Pearson Prentice Hall 2013

17.  Note: ◦ Public key/private key pairs (discussed later in the chapter) must be much longer than symmetric keys to be considered to be strong because of the disastrous consequences that could occur if a private key is cracked and because private keys cannot be changed frequently. Public keys and private keys must be at least 512 to 1,024 bits long 17 Copyright Pearson Prentice Hall 2013

18. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 18 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

19. 19 RC4DES3DESAES Key Length (bits) 40 bits or more 56112 or 168128, 192, or 256 Key StrengthVery weak at 40 bits WeakStrong Processing Requirements LowModerateHighLow RAM Requirements LowModerate Low RemarksCan use keys of variable lengths Created in the 1970s Applies DES three times with two or three different DES keys Today’s gold standard for symmetric key encryption

20. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 20 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

21.  Cryptographic Systems ◦ Encryption for confidentiality is only one cryptographic protection ◦ Individual users and corporations cannot be expected to master these many aspects of cryptography ◦ Consequently, crypto protections are organized into complete cryptographic systems that provide a broad set of cryptographic protection 21 Copyright Pearson Prentice Hall 2013

22.  Cryptographic Systems 1.Two parties first agree upon a particular cryptographic system to use 2.Each cryptographic system dialogue begins with three brief handshaking stages 3.The two parties then engage in cryptographically protected communication  This ongoing communication stage usually constitutes nearly all of the dialogue 22 Copyright Pearson Prentice Hall 2013

23. 23 Copyright Pearson Prentice Hall 2013

24. Copyright Pearson Prentice-Hall 201024

25. 25 Copyright Pearson Prentice Hall 2013

26. 26 Cipher SuiteKey Negotiation Digital Signature Method Symmetric Key Encryption Method Hashing Method for HMAC Strength NULL_WITH_NULL_NULLNone RSA_EXPORT_WITH_ RC4_40_MD5 RSA export strength (40 bits) RC4 (40-bit key) MD5Weak RSA_WITH_DES_CBC_ SHA RSA DES_CBCSHA-1Stronger but not very strong DH_DSS_WITH_3DES_ EDE_CBC_SHA Diffie– Hellman Digital Signature Standard 3DES_ EDE_CBC SHA-1Strong RSA_WITH_AES_256_CB C_SHA256 RSA AES 256 bits SHA-256Very strong Copyright Pearson Prentice Hall 2013

27. Copyright Pearson Prentice-Hall 201027

28. Copyright Pearson Prentice-Hall 201028

29. 29 Copyright Pearson Prentice Hall 2013

30. Copyright Pearson Prentice-Hall 2010 30 Supplicant: Wishes to prove its identity Verifier: Tests the credentials, accepts or rejects the supplicant Credentials Proofs of identity (password, etc.)

31. Copyright Pearson Prentice-Hall 201031

32.  Hashing ◦ A hashing algorithm is applied to a bit string of any length ◦ The result of the calculation is called the hash ◦ For a given hashing algorithm, all hashes are the same short length 32 Bit string of any length Hash: bit string of small fixed length Hashing Algorithm Hashing Algorithm Copyright Pearson Prentice Hall 2013

33.  Hashing versus Encryption 33 CharacteristicEncryptionHashing Result lengthAbout the same length as the plaintext Short fixed length regardless of message length Reversible?Yes. DecryptionNo. There is no way to get from the short hash back to the long original message Copyright Pearson Prentice Hall 2013 Well Kind-of……

34. Copyright Pearson Prentice Hall 2013 34

35. 35 Copyright Pearson Prentice Hall 2013

36. 36 Copyright Pearson Prentice Hall 2013

37. Copyright Pearson Prentice-Hall 2010  Hashing Algorithms ◦ MD5 (128-bit hashes) MD5 ◦ SHA-1 (160-bit hashes) SHA-1 ◦ SHA-224, SHA-256, SHA-384, and SHA-512 (name gives hash length in bits) ◦ Note: MD5 and SHA-1 should not be used because have been shown to be unsecure 37

38. 38 Copyright Pearson Prentice Hall 2013

39.  There are two types of ciphers used for confidentiality ◦ In symmetric key encryption for confidentiality, the two sides use the same key  For each dialogue (session), a new symmetric key is generated: the symmetric session key ◦ In public key encryption, each party has a public key and a private key that are never changed  A person’s public key is available to anyone  A person keeps his or her private key secret  Two common ciphers  RSA (most common)  elliptic curve cryptography (I think UCF uses this) 39 Copyright Pearson Prentice Hall 2013

40. Copyright Pearson Prentice-Hall 2010 40 Digital Certificates

41. 41 Copyright Pearson Prentice Hall 2013

42. Copyright Pearson Prentice-Hall 2010 42

43.  How do you exchange the key(s) necessary for encryption?  Solution: ◦ Diffie-Hellman math – don’t ask me to explain  Requirements:  p and q ◦ Two random very large numbers 100’s of digits long or longer  n = p * q ◦ if p and q are sufficiently large it is almost impossible to factor n and come up with p and q; thus almost impossible to determine d!  d = private key; derived from p and q (see wikipedia)see wikipedia  e = public key; derived from p and q (see wikipedia)see wikipedia

44.  Plaintext Message = M  Convert PlainText to number (binary) = M  M^e (mod n) = CipherText(C) ◦ e and n are publicly known, either sent to party for communication or stored publicly (CA’s)  C^d (mod n) = M

45. 45

46.  What is the weakest link in RSA?

47.  What did security researchers allege?  Were they right?  What is a Pseudo-Random Number Generator?  What size key’s should be in use today?

48.  The two parties exchange parameters p and g  Each uses a number that is never shared explicitly to compute a second number ◦ Each sends the other their second number  Each does another computation on the second computed number  Both get the third number, which is the key  All of this communication is sent in the clear 48 Copyright Pearson Prentice Hall 2013

49. Copyright Pearson Prentice-Hall 2010 49 The gory details The gory details

50. Copyright Pearson Prentice-Hall 201050

51. 51 Copyright Pearson Prentice Hall 2013

52.  Consumes nearly all of the dialogues  Message-by-Message Encryption ◦ Nearly always uses symmetric key encryption ◦ Already covered ◦ Public key encryption is too inefficient  Message-by-Message Authentication ◦ Digital signatures ◦ Message authentication codes (MACs) ◦ Also provide message-by-message integrity 52 Copyright Pearson Prentice Hall 2013

53. Copyright Pearson Prentice-Hall 201053

54. 54 Copyright Pearson Prentice Hall 2013

55. 55 Encryption is done to protect the plaintext It is not needed for message-by-message authentication Encryption is done to protect the plaintext It is not needed for message-by-message authentication Copyright Pearson Prentice Hall 2013

56. 56 Copyright Pearson Prentice Hall 2013

57. 57 Encryption GoalSender Encrypts with Receiver Decrypts with Public Key Encryption for Confidentiality The receiver’s public key The receiver’s private key Public Key Encryption for Authentication The sender’s private key The True Party’s public key (not the sender’s public key) Point of frequent confusion Copyright Pearson Prentice Hall 2013

58.  Cannot use the sender’s public key ◦ It would always “validate” the sender’s digital signature  Normally requires a digital certificate ◦ File provided by a certificate authority (CA)  The certificate authority must be trustworthy ◦ Digital certificate provides the subject’s (True Party’s) name and public key ◦ Don’t confuse digital signatures and the digital certificates used to test digital signatures! 58 Copyright Pearson Prentice Hall 2013

59. 59 FieldDescription Version Number Version number of the X.509 standard. Most certificates follow Version 3. Different versions have different fields. This figure reflects the Version 3 standard. IssuerName of the Certificate Authority (CA). Serial Number Unique serial number for the certificate, set by the CA. Subject (True Party) The name of the person, organization, computer, or program to which the certificate has been issued. This is the true party. Public KeyThe public key of the subject (the true party). Public Key Algorithm The algorithm the subject uses to sign messages with digital signatures. Certificate provides the True Party’s public key Serial number allows the receiver to check if the digital certificate has been revoked by the CA Copyright Pearson Prentice Hall 2013

60. 60 FieldDescription Digital Signature The digital signature of the certificate, signed by the CA with the CA’s own private key. For testing certificate authentication and integrity. User must know the CA’s public key independently. Signature Algorithm Identifier The digital signature algorithm the CA uses to sign its certificates. Other Fields… The CA signs the cert with its own private key so that the cert’s validity can be checked for alterations. Copyright Pearson Prentice Hall 2013

61.  sign e-mails  ensure documents haven't been tampered with  verify that software and software updates available online originated with a particular person or group Copyright Pearson Prentice-Hall 2010 61

62.  Testing the Digital Signature ◦ The digital certificate has a digital signature of its own ◦ Signed with the Certificate Authority’s (CA’s) private key ◦ Must be tested with the CA’s well-known public key ◦ If the test works, the certificate is authentic and unmodified 62 Copyright Pearson Prentice Hall 2013

63.  Checking the Valid Period ◦ Certificate is valid only during the valid period in the digital certificate (not shown in the figure) ◦ If the current time is not within the valid period, reject the digital certificate 63 Copyright Pearson Prentice Hall 2013

64.  Checking for Revocation ◦ Certificates may be revoked for improper behavior or other reasons ◦ Revocation must be tested ◦ Cannot be done by looking at fields within the certificate ◦ Receiver must check with the CA 64 Copyright Pearson Prentice Hall 2013

65.  Checking for Revocation ◦ Verifier may download the entire certificate revocation list from the CA  See if the serial number is on the certificate revocation list  If so, do not accept the certificate ◦ Or, the verifier may send a query to the CA  Requires the CA to support the Online Certificate Status Protocol 65 Copyright Pearson Prentice Hall 2013

66. 66 Copyright Pearson Prentice Hall 2013

67.  Twitter.com Twitter.com Copyright Pearson Prentice-Hall 2010 67

68.  Used counterfeit Microsoft digital certificate  Allowed attackers to “sign” Flame software as if it was Microsoft Software ◦ Thus able to evade Malware detection  How? ◦ Cryptographic Collision Attack  Hashing plaintext should result in a unique hash  But sometimes independent plaintext results in the same hash  If you know this you can reverse engineer hash key and counterfeit a certificate based on hash Copyright Pearson Prentice-Hall 2010 68

69.  Also Brings Message Integrity ◦ If the message has been altered, the authentication method will fail automatically  Digital Signature Authentication ◦ Uses public key encryption for authentication ◦ Very strong but expensive  Key-Hashed Message Authentication Codes ◦ An alternate authentication method using hashing ◦ Much less expensive than digital signature authentication ◦ Much more widely used 69 Copyright Pearson Prentice Hall 2013

70. 70 Copyright Pearson Prentice Hall 2013

71. 71 As in the case of digital signatures, confidentiality is done to protect the plaintext. It is not needed for authentication and has nothing to do with authentication. As in the case of digital signatures, confidentiality is done to protect the plaintext. It is not needed for authentication and has nothing to do with authentication. Copyright Pearson Prentice Hall 2013

72. 72 Copyright Pearson Prentice Hall 2013

73.  Nonrepudiation means that the sender cannot deny that he or she sent a message  With digital signatures, the sender must use his or her private key ◦ It is difficult to repudiate that you sent something if you use your private key  With HMACs, both parties know the key used to create the HMAC ◦ The sender can repudiate the message, claiming that the receiver created it 73 Copyright Pearson Prentice Hall 2013

74.  However, packet-level nonrepudiation is unimportant in most cases  The application message—an e-mail message, a contract, etc., is the important thing  If the application layer message has its own digital signature, you have nonrepudiation for the application message, even if you use HMACs at the Internet layer for packet authentication 74 Copyright Pearson Prentice Hall 2013

75.  Replay Attacks ◦ Capture and then retransmit an encrypted message later ◦ May have a desired effect ◦ Even if the attacker cannot read the message 75 Copyright Pearson Prentice Hall 2013

76.  Thwarting Replay Attacks ◦ Time stamps to ensure freshness of each message ◦ Sequence numbers so that repeated messages can be detected ◦ Nonces  Unique randomly generated number placed in each request message  Reflected in the response message  If a request arrives with a previously used nonce, it is rejected 76 Copyright Pearson Prentice Hall 2013

77. Copyright Pearson Prentice-Hall 2010Copyright Pearson Prentice-Hall 2009 77 ConfidentialityAuthentication Symmetric Key Encryption Applicable. Sender encrypts with key shared with the receiver. Not applicable. Public Key Encryption Applicable. Sender encrypts with receiver’s public key. Receiver decrypts with the receiver’s own private key. Applicable. Sender (supplicant) encrypts with own private key. Receiver (verifier) decrypts with the public key of the true party, usually obtained from the true party’s digital certificate. HashingNot applicable.Applicable. Used in MS-CHAP for initial authentication and in HMACs for message-by- message authentication.

78. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 78 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

79.  Quantum Mechanics ◦ Describes the behavior of fundamental particles ◦ Complex and even weird results 79 Copyright Pearson Prentice Hall 2013

80.  Quantum Key Distribution ◦ Transmits a very long key—as long as the message ◦ This is a one-time key that will not be used again ◦ A one-time key as long as a message cannot be cracked by cryptanalysis ◦ If an interceptor reads part of the key in transit, this will be immediately apparent to the sender and receiver 80 Copyright Pearson Prentice Hall 2013

81.  Quantum Key Cracking ◦ Tests many keys simultaneously ◦ If quantum key cracking becomes capable of working on long keys, today’s strong key lengths will offer no protection 81 Copyright Pearson Prentice Hall 2013

82. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 82 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

83. 83 Copyright Pearson Prentice Hall 2013

84. 84 Copyright Pearson Prentice Hall 2013

85. 3.1 What Is Cryptography 3.2 Symmetric Key Encryption Ciphers 3.3 Cryptographic System Standards 3.4 The Negotiation Stage 3.5 Initial Authentication Stage 3.6 The Keying Stage 3.7 Message-by-Message Authentication 85 3.8 Quantum Security 3.9 Cryptographic Systems 3.10 SSL/TLS and IPsec Copyright Pearson Prentice Hall 2013

86. 86 Copyright Pearson Prentice Hall 2013

87. 87 Copyright Pearson Prentice Hall 2013

88. 88 SSL/TLSIPsec Cryptographic security standardYes Cryptographic security protectionsGoodGold Standard Supports central managementNoYes Complexity and expenseLowerHigher Layer of operationTransportInternet Transparently protects all higher-layer traffic NoYes Works with IPv4 and IPv6NAYes Modes of operationNATransport, Tunnel Copyright Pearson Prentice Hall 2013

89. 89 1. End-to-End Security (Good) 1. End-to-End Security (Good) 2. Security in Site Network (Good) 2. Security in Site Network (Good) 3. Setup Cost On Each Host (Costly) 3. Setup Cost On Each Host (Costly) Copyright Pearson Prentice Hall 2013

90. 90 2. No Security in Site Network (Bad) 2. No Security in Site Network (Bad) 3. No Setup Cost On Each Host (Good) 3. No Setup Cost On Each Host (Good) Copyright Pearson Prentice Hall 2013

91. 91 CharacteristicTransport ModeTunnel Mode Uses an IPsec VPN Gateway? NoYes Cryptographic Protection All the way from the source host to the destination host, including the Internet and the two site networks. Only over the Internet between the IPsec gateways. Not within the two site networks. Setup CostsHigh. Setup requires the creation of a digital certificate for each client and significant configuration work. Low. Only the IPsec gateways must implement IPsec, so only they need digital certificates and need to be configured. Copyright Pearson Prentice Hall 2013

92. 92 CharacteristicTransport ModeTunnel Mode Firewall FriendlinessBad. A firewall at the border to a site cannot filter packets because the content is encrypted. Good. Each packet is decrypted by the IPsec gateway. A border firewall after the IPsec gateway can filter the decrypted packet. The “Bottom Line”End-to-end security at high cost. Low cost and protects the packet over the most dangerous part of its journey. Copyright Pearson Prentice Hall 2013

93. 93 Copyright Pearson Prentice Hall 2013

94. 94

95. Copyright © 2013 Pearson Education, Inc. Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall